Radiation therapy (also referred to as radiotherapy) may be used in the treatment of cancer or other pathologies. Radiotherapy involves delivering a prescribed dose of radiation to a target region of a patient, for example, to a tumor or other cancerous tissue. The target region may be imaged prior to the administration of radiotherapy, and a radiotherapy treatment plan (“treatment plan”) may be formulated based on, e.g., the shape, size, location, and/or orientation of the target and the surrounding structures, among other things. A radiotherapy delivery device may then be used to deliver radiation to the target region of the patient, in accordance with the treatment plan.
Traditionally, for each patient, a treatment plan may be created based on clinical and dosimetric objectives and constraints (e.g., the maximum, minimum, and mean doses of radiation to the tumor and surrounding organs). The treatment planning procedure may include using a three-dimensional (3D) image of the patient to identify a target region (e.g., the tumor) and to identify critical organs near the tumor.
After initial images of the target are acquired, however, the shape of the target region may change. For example, a patient may move voluntarily or involuntarily due to regular biological processes, including, e.g., breathing, swallowing, blinking, twitching, peristalsis, digestion, filling of the bladder, beating of the heart, or other movements. These movements may compress and/or otherwise deform or re-shape the target region. While systems exist for tracking the movement of a target region, this tracking generally only accounts for changes in the location of a target region in the body. Current systems assume a constant shape of the target region during the movement being tracked, i.e., they assume that the target region is rigid. Often, however, tumors or other cancerous growths are formed of soft tissue and may be deformed by normal body processes. Currently available systems may not be able to track changes to the actual shape of the target region that may occur between treatment planning and radiotherapy or during radiotherapy.
Changes in the shape of the target region that are not accounted for may reduce the efficacy of radiotherapy. For example, if the shape of the target region is different than the assumed shape based on prior imaging, then an incorrect dose of radiation may be delivered to the intended target region or portions of the target region may be missed entirely. Additionally, surrounding healthy structures may receive radiation instead of, or in addition to, the intended target region. Exposing the wrong area to radiation may ultimately harm or kill surrounding healthy cells. Accordingly, there is a need for systems and methods capable of accounting for variations in the shape of a target region during radiotherapy. There is a need for systems and methods of generating a motion target volume for use during radiotherapy that accounts for changes in the shape of the target region when tracking the delivery of radiation.